Bone grafting is widely used to treat fractures, non-unions and to induce arthrodeses. Autogenous cancellous bone, which is taken from one site in the graftee and implanted in another site in the graftee, is currently the most effective bone graft. Autogenous cancellous bone provides the scaffolding to support the distribution of the bone healing response, and progenitor cells which form new cartilage or bone. However, harvesting autogenous bone results in significant cost and morbidity, including scars, blood loss, pain, prolonged operative and rehabilitation time and risk of infection. Furthermore, the volume of the graft site can exceed the volume of available autograft.
Accordingly, alternatives to autografts have been developed. Several purified or synthetic materials, including ceramics, biopolymers, processed allograft bone and collagen-based matrices have been investigated or developed to serve as substitutes for autografts. The FDA has approved a porous coral-derived synthetic hydroxyapatite ceramic for use in contained bone defects. A purified collagen/ceramic composite material is also approved for use in acute long bone fractures. Although these materials avoid the morbidity involved in harvesting autografts and eliminate problems associated with a limited amount of available autograft, the clinical effectiveness of the synthetic materials remains generally inferior to autografts. The synthetic graft materials have also been used as carriers for bone marrow cells. When the above composite materials are implanted into skeletal defects, progenitor cells differentiate into skeletal tissue.
In some instances, composite implants are made by combining a synthetic graft material in a cell suspension with a similar or lesser volume obtained from a bone marrow aspirate. However, the progenitor cells, which have the capacity to differentiate into cartilage, bone, muscle, fibrous tissue, and other connective tissue, are present in the bone marrow in very miniscule amounts. The numbers of progenitor cells present in 1 ml of bone marrow varies widely between patients from about 100 cells to 20,000 cells. This represents a mean of about one in 20,000 to one in 40,000 of the nucleated cells in a bone marrow aspirate. Thus, a composite implant made by combining a given volume of synthetic graft material in a comparable volume of fresh bone marrow contains relatively few progenitor cells.
Accordingly, a technique has been previously developed to increase the relative concentration of progenitor cells in composite implants. This technique involves plating a suspension of bone marrow cells onto tissue culture dishes, culturing the cells in a select medium for one or more days to achieve an enhanced population of progenitor cells, and then detaching the cells from the tissue culture dishes to provide a cell suspension containing an increased population of progenitor cells. Composite implants are then made by soaking synthetic ceramic carriers in this progenitor cell enriched suspension. Unfortunately, this method of preparing composite implants is very time consuming. Moreover, if the original progenitor culture cells are derived from bone marrow aspirates obtained from the graftee, the graftee must undergo multiple invasive procedures; one procedure to remove his or her bone marrow, and another procedure on a later date to implant the composite graft. Consequently, the graftee may be exposed to anesthesia more than once.
Another technique has also been developed to produce a composite bone graft matrix having the benefits of the culture method, but is not so time consuming and does not require multiple invasive procedures. In this technique, a composite matrix having an enriched population of progenitor cells is produced by contacting a particular volume of matrix material with an excess volume of bone marrow aspirate (see U.S. Pat. Nos. 5,824,084 and 6,049,026). In that technique, bone marrow aspirate containing progenitor cells is passed through a porous matrix material having a surface which selectively bonds to progenitor cells, thus retaining the progenitor cells within the matrix and allowing excesses of other cells (such as blood cells and other nucleated marrow-derived cells) to pass through. The now progenitor cell-enriched graft matrix is implanted in a patient.
However, because progenitor cells are so strongly and selectively bonded to some matrix surfaces (e.g. allograft bone matrix), they are nonuniformly distributed throughout the matrix, with dense pockets of progenitor cells discretely concentrated in the vicinity of initial contact between the marrow aspirate and the matrix material. Consequently, a bone graft prepared by this technique suffers from the limitation that bone healing subsequent to implantation does not occur uniformly due to the nonuniform distribution of progenitor cells within the implanted matrix. Additionally, bone healing subsequent to implantation of the matrix occurs relatively slowly.
It is therefore desirable to have a new method of preparing composite bone marrow graft material having an enriched population of progenitor cells which can be performed intraoperatively, i.e. at the same time bone marrow is being taken from the graftee, that results in uniform distribution of progenitor cells throughout the graft material, and that facilitates accelerated healing upon implantation.
A composite bone marrow graft material is provided comprising a porous biocompatible implantable matrix and clot material. The composite bone marrow graft material has an enriched population of progenitor cells. A method of preparing composite bone marrow graft material is also provided. The method includes the steps of providing a bone marrow aspirate, providing a porous biocompatible implantable matrix, contacting the bone marrow aspirate and the matrix to provide an enriched matrix, and mechanically mixing the enriched matrix to yield a composite bone marrow graft material having progenitor cells distributed substantially uniformly throughout the composite bone marrow graft material.
A kit for the preparation of composite bone marrow graft material is also provided. The kit includes a matrix container, a first endcap, and a first loading syringe. The first loading syringe is adapted to mate to the first endcap to provide fluid communication between the first loading syringe and the matrix container. The first endcap is releasably attachable to the matrix container.